Technical Field
This disclosure relates to an automatic repeat request method, and more particularly to a hybrid automatic repeat request method.
Related Art
Long term evolution (LTE) and the fourth generation (4G) communication technologies are high-speed wireless communication protocols applied to mobile phones and data terminals in the current telecommunications. In these communication technologies, the application of a hybrid automatic repeat request (HARQ) provides a data retransmission mechanism with high efficiency. The HARQ combines the technologies of forward error correction (FEC) and automatic repeat request (ARQ), and includes transmitting data from a base station to user equipment and receiving a feedback signal from the user equipment to determine whether to retransmit the data.
Taking the HARQ in the LTE architecture as an example, please refer to FIGS. 1A-1C, wherein FIGS. 1A-1C are timing diagrams of the transmission of one or more data packets according to the related art. As shown in FIG. 1A, in the LTE architecture, an ideal time interval between the step of data transmission performed by a base station eNB and the step of returning a feedback signal performed by the user equipment UE is 4 subframes, and an ideal time interval between the step of returning the feedback signal performed by the user equipment UE and the step of retransmitting the old data or transmitting new data performed by the base station eNBu according to the feedback signal is also 4 subframes. Therefore, the HARQ involves in eight parallel HARQ process HP0-HP7 through frequency-division duplexing. These HARQ process HP0-HP7 start to transmit data from the base station eNB respectively in the subframes n−n+7, transmit feedback signals from the user equipment UE respectively in the subframes n+4−n+11, retransmit the old data or transmit new data from the base station eNB respectively in the subframes n+8−n+15, transmit feedback signals corresponding to the last transmitted data from the user equipment UE, and so on.
However, in practice, as shown in FIG. 1B, the base station eNB includes a medium access control layer eNB_MAC, a physical layer eNB_PHY and a wireless communication layer eNB_RF. When the medium access control layer eNB_MAC and the physical layer eNB_PHY have a communication connection therebetween via a fronthaul network FH, the frounthaul network FH must generate a latency L so that the HARQ process cannot complete a cycle in 8 subframes. For example, if the latency L occupies two subframes, the HARQ process HP0 firstly starts to transmit data from the wireless communication layer eNB_RF to the user equipment UE in the subframe n, and the user equipment UE returns an ACK signal in the subframe n+4 for asking for new data. Due to the latency L of the fronthaul network FH, the wireless communication layer eNB_RF cannot transmit new data until the subframe n+12. Because there are merely eight parallel HARQ processes HP0-HP7, the wireless communication layer eNB_RF and the user equipment UE must be in the idle state for 4 subframes as shown in FIG. 1C, so that the throughput in this case must be much lower than an ideal throughput.
Furthermore, when the central processing unit where the physical layer eNB_PHY is disposed has a low processing speed, a latency must be generated so that the throughput of the user equipment must be low.